I have been longtime fan of getting myself a 3d printer but they were way too expensive usually. Then I stumbled upon Tom's youtube vids on dolly. Big cheers for those

Anyhow. Now that I have finally managed to scrape all the pieces and build the damn thing, I seem to have hit a snag.. When I tried to pidtune my hotend, I heard a pop and whole printer went dead. (Not the arduino mind you, just steppers and such).

Since going budget was quite the sales point I did just that and seems like I might have gotten some shoddy chinese quality.

And then the problem.

I presume it's not quite right if I measure resistance from heat cartridge leads and it shows 0.7 ohms, kinda think this is the culprit that blew my 5A (?) smd fuse from my biquitech "1.6 ramps" board.. Not sure if it caused more damage on that board among that fuse.. Assuming I didnt fry the ramps board, should be fine just replacing the fuse right?

Now another question is, since it's still quite a tight budget.. I need working cartridge to replace the faulty one.. Any tips where (in Europe) I might look for one with modest price (and postage that doesnt double the fee), destination this nordic wonderland of Finland?

I could always go back to aliexpress or some other chinese site and get one. But I've kinda talked about making a blog post(s) on building this printer to my school friends and I dont really fancy waiting another 2++ weeks for a part to arrive from asia..

Oh and third question, since this 1.6 ramps board only has one input for power, is my 16A 12V atx psu enough for driving a printer or should I look for some "real" 20A++ psu?

Last edited by MikaTuunanen on Wed Nov 07, 2018 1:12 am, edited 2 times in total.

If your heated bed have realy 0.7 Ohm (it can be correct) in a circuit, according to ohm's law it must drains more then 17 Amps (17.14 to be precise) which is more then your 16 Amp power source can handle for a long time... and it is also a hell of a current for most chinese mosfets (and fuses, resistors etc.) ... even that fancy RAMPs board Moorviper suggest, have fuse for heated bed rated only for 11 Amps and even connector is only for 15 Amps (accornding to description).

In this case:
First I suggest you mainly better power source. I am not really sure if even 20 Amps will be enough because I don't know rest of your setup... but hotend is about 30 to 40W so 2.5 - 3.5 Amp and steppers 1 to 2 Amp each, some peanutes for supplying the electronics... in worst scenario it is about 25 to 30A in peak if i am correct.
And second I suggest to add solid state relay (driven by your ramps mosfet) for your 200W heated bed whatever board you choose for the job. That will dramaticly decrease curents on your RAMPs and increase safety of this setup.

And about your blown up RAMPs board... if it survived and only fuse was popped, there will be probably one (that 5A) for electronics (and motors?) and second (not sure by rating but expecting something similar to another RAMPs so probably 11Amp) for your heated bed circuit. You can start there.

If your heated bed have realy 0.7 Ohm (it can be correct) in a circuit, according to ohm's law it must drains more then 17 Amps (17.14 to be precise) which is more then your 16 Amp power source can handle for a long time... and it is also a hell of a current for most chinese mosfets (and fuses, resistors etc.) ... even that fancy RAMPs board Moorviper suggest, have fuse for heated bed rated only for 11 Amps and even connector is only for 15 Amps (accornding to description).

No, my heated bed is ~1.3 ohms and is just fine. Kirchoff states that it pulls somewhere around 9 amps.. Hence reason it failed pidtune @ 90C I presume (80C it can reach and stay stable) - it aint that powerful (~110W), but I'm sure it's enough for my needs to start, aint going to touch ABS for a while and PETG should be fine too as PLA.

(Newbie question to this part - does heated bed need to be heated through whole print or just first n layers to ensure it sticks?)

Problem was (is) heater cartridge on hotend, which I'm pretty sure (tho I'm a new to the 3d printing scene) isnt supposed to be <1 ohm.. Especially if it's advertised as 12V/40W (being ~on par with the heated bed)
Thankfully, that site Mooviper suggested above for that somewhat better looking ramps board, had cheap cartridges so I ordered one up and cross my fingers I get it by Friday.. Not to mention there were Pinda (legit? clone?) probe too which I hastily ordered wrong type/size originally for the printer..

First I suggest you mainly better power source. I am not really sure if even 20 Amps will be enough because I don't know rest of your setup...

I'll add better psu to upgrade list but first I wanna see how far this old atx psu gets me.. My setup itself isnt anything fancy and (fingers crossed) should do just fine.. Pretty much following what Tom suggested on his dolly page.. Yet again, one trick pony PSU wouldnt have useless cables laying around and might be bit slimmer to actually fit on the frame like on original i3.. On the other hand, I like the idea that I can wire ATX psu to raspberry that it turns on when needed without user intervention.. Choices, choices.. Restricted by finances..

And second I suggest to add solid state relay (driven by your ramps mosfet) for your 200W heated bed whatever board you choose for the job. That will dramaticly decrease curents on your RAMPs and increase safety of this setup.

This certainly is going to happen when I find myself able to get MK42.

And about your blown up RAMPs board... if it survived and only fuse was popped, there will be probably one (that 5A) for electronics (and motors?) and second (not sure by rating but expecting something similar to another RAMPs so probably 11Amp) for your heated bed circuit. You can start there.

Well by eyeing the board (without magnifying glass - damn things are never be found when you need 'em) it didnt suffer anything else than that 5A smd fuse which blew due that faulty heater cartridge when trying to pidtune hotend. So at first I'll just see if I can get it replaced with a fresh one.

Oh, my fault, I missed that it was during hotend PID tuning and for some unknown reason (probably becasuse of the calucated power) I mixed up hotend and heated bed resistance... then yes... it will be probably the 5A fuse, becaouse in that case your hot end burns about 200W which is really mad.
As you mentioned, hot end cartrige depends on a designed power (30 to 40W) should be about let's say from 3.5 to 5 ohm.

In the light of (for me) new facts... still I will advise to pick better powersource... I know that 5VSB (is it enough for supplying RPi?) rail and direct access to switching your PSU via existing pins sounds great but... may be for printing PLA where you will need less power for your heated bed will be okay but for a higher temperature of different filamet it will probably run on the edge. If you can directly measure how much it drains from main (or your PSU) you can calculate the approximate load of your PSU and decide. But there is still a not expensive solution where you will use 5V powersuply for your RPi and another solid state relay.

Because I had issues with elephant foot effect... I tried to lower bed temp for PLA form 60°C on start to 50°C during print. But in that case I start to suffer by thermal expansion, deformations and lost of adhesion. So changing temp during print... well not good idea for me on PLA... but I am also a kind of newbie so it can be different for another filament. But as i learned... if you will print only PLA there is still possibility to print without heat bed at all (but have no experience with that so I don't know how you should prepare print surface for that for good adheasion as i remember bluetape should work but...).

I hate that soldered fuses... it is so inpractical. It expect that probably nothing gona happend but... If there is a place and you are good with soldering gun... you also can replace it with some fuse holder and use replacable fuse... then according to murphy's law you can expect that you will never need to replace it again.

As you mentioned, hot end cartrige depends on a designed power (30 to 40W) should be about let's say from 3.5 to 5 ohm.

Yep. The shoddy chinese quality strikes again and claims another victim. Should have suspected something when I noticed the cartridge had some dents on the end. And certainly should have checked the resistance. Lesson learned.

In the light of (for me) new facts... still I will advise to pick better powersource... I know that 5VSB (is it enough for supplying RPi?) rail and direct access to switching your PSU via existing pins sounds great but... may be for printing PLA where you will need less power for your heated bed will be okay but for a higher temperature of different filamet it will probably run on the edge.

Came to think about that external mosfet.

That ATX power supply I have is 250W and it has 12V rail spliced to 2 rails - 14A and 16A respectively. I currently can only use one since that 1.6 ramps has only one power input and those rails arent uniform amps so cant really paraller them and they both have their own protection circuit for OVP, UVP, OCP, OPP and SCP. But if I get myself external mosfet, I can put the 14A rail through that for heated bed and keep that 16A rail still on ramps for steppers+hotend? Should work? And should allow for better heating bed in the future - especially if I change PSU and/or switch to 24V.

What comes to raspberry, ATX supply's 5VSB should be enough for it. But since my raspberry is already doing other stuff, octoprint would just be in addition to it's tasks already, I would still run it through different power. Doesnt exclude using it to power up the PSU tho when needed for printing.

If you can directly measure how much it drains from main (or your PSU) you can calculate the approximate load of your PSU and decide.

Well it's just a matter of putting the PSU behind a meter and having a working printer. By next week I can check how hungry it is. *fingers crossed*

Because I had issues with elephant foot effect... I tried to lower bed temp for PLA form 60°C on start to 50°C during print. But in that case I start to suffer by thermal expansion, deformations and lost of adhesion. So changing temp during print... well not good idea for me on PLA... but I am also a kind of newbie so it can be different for another filament. But as i learned... if you will print only PLA there is still possibility to print without heat bed at all (but have no experience with that so I don't know how you should prepare print surface for that for good adheasion as i remember bluetape should work but...).

Well my heated bed thankfully can hold 80C just fine. So should be on good side with PLA/PETG with it. And if I change it behind external mosfet it helps the load on ramps. So most likely I'll step on that road.

I hate that soldered fuses... it is so inpractical. It expect that probably nothing gona happend but... If there is a place and you are good with soldering gun... you also can replace it with some fuse holder and use replacable fuse... then according to murphy's law you can expect that you will never need to replace it again.

Yeah. They do suck. I'm going to go consult electronics teacher at my school today and see what he thinks is the best route. Problem with fuse holder is that there's really not much room to put on there and I dont know if the board could be drilled through for leads to get the fuse holder off board.
Bigtreetech claims the board to be 4 layers. And below is one drawing of it. Might work, might not. Not that familiar with multilayer pcb's.

Which ever road is chosen in replacing the fuse, there are decent enough equipment at school to do the trick. (Yay for finnish educational system)

Thankfully, that site Mooviper suggested above for that somewhat better looking ramps board, had cheap cartridges so I ordered one up and cross my fingers I get it by Friday.. Not to mention there were Pinda (legit? clone?) probe too which I hastily ordered wrong type/size originally for the printer.

...and apparently I should have googled them before making the order.. I made it 06.11.2018 (european format).. and that site still only acknowledges my order as "yay, we've got your money" and nothing else.. *sigh* Ordering straight from China myself and those parts would soon be here vs. not a clue when they even ship 'em..

Well, on a positive note, my ramps was left with our electronics teachers and they said they'll look into if they have a replacement fuse 8-p.. Should know today which way it goes..